when i switch thermostat to 30 (max) radiators are not really hot i have disconnected it once before but cudnt get heating on at all so had to reconnect it its a honeywell just a circle basic one with 5c to 30c is there something am doing wrong or cant they be disconnected thanks.
The thermostat works by connecting the wires together when there is demand for heat. Simply removing the thermostat from the wall and connecting the two wires together will fire the boiler. I am assuming here that the thermostat is a simply voltage free type in other words has no power to it as most of the combi boilers are these days.
If you are talking about a room thermostat which you appear to be then disconnecting and shorting it out should not really have the effect you are looking for ie hotter radiators. If your system is up to par turning the boiler stat up should have the effect of not being able to keep your hands on the radiators. I would suggest there is more to this than a room stat. If you can contact the installer or get another Gas Safe engineer in to check over the system.
The expression volt free only refers to the contact before you use it. When wires are connected there will be volts in them. I would guess that the four wires are earth, live ,switched live ,and accelerator neutral but could be 1pair supply volts 1 pair relay switch supply volts could be mains or low voltage. Get a meter to check before connecting any together.
